NMR OF ROOM-TEMPERATURE SAMPLES WITH A FLUX-LOCKED DC SQUID

Superconducting quantum interference devices (SQUID's) are the most se nsitive detectors of magnetic fields. Since SQUID's detect the magneti c flux rather than its rate of change, they can be used to great advan tage to measure nuclear magnetic resonance (NMR) signals at low fields and frequencies, We have used a de (direct-current) SQUID operated in flux-locked mode to significantly improve upon our previous low-field NMR results performed using an RF (radio-frequency) SQUID. The increa se in sensitivity gained by using the de SQUID has helped in reducing the signal acquisition time by a factor of more than 100 compared with our earlier measurements using an RF SQUID. We have also obtained a s imple one-dimensional T-1-contrasted NMR image of a two-component samp le consisting of mineral oil and tap water at room temperature. Our re sults highlight the sensitivity of the SQUID as an NMR detector and th e promise of using SQUID's in NMR imaging at low fields for both medic al applications and for materials' nondestructive evaluation.